A dangerous heart rate is one that falls outside the healthy range for your body, and doctors say identifying the difference between normal variation and a medical issue can save lives.
The heart pumps blood to deliver oxygen and nutrients throughout the body. A normal adult heart rate typically falls between 60 and 100 beats per minute, but this range isn’t a strict rule for everyone. A well-trained athlete might have a resting rate in the 50s or even 40s without any cause for concern.
Heart rate varies based on several factors, including age, fitness level, temperature, and stress. “It is good to have variability in your heart rates depending on what you are doing,” says Puja Mehta, M.D., director of Women’s Translational Cardiovascular Research at the Emory Women’s Heart Center. “When we sleep, it is normal for heart rates to be lower.”
Children generally have faster heart rates than adults. Newborns can range from 70 to 190 beats per minute, with averages decreasing as they approach school age. A resting rate of over 90 beats per minute may indicate an underlying issue such as anemia, dehydration, or thyroid disease, according to Ronald Freudenberger, M.D., a cardiologist and former physician in chief at Lehigh Valley Heart and Vascular Institute.
When to worry about a high rate
A resting heart rate greater than 100 beats per minute is known as tachycardia. If untreated, this condition can put excess strain on the heart muscle by overworking it, potentially leading to abnormal heart enlargement and weakening, says Dr. Mehta.
While occasional elevations during exercise or stress are normal, a rate consistently above 110 beats per minute—without an obvious cause like vigorous activity—warrants a check-up. “People who have heart rhythm disturbances also can have a high heart rate—the most common being atrial fibrillation,” Dr. Freudenberger notes.
The danger zone for low rates
Conversely, a dangerously low heart rate, or bradycardia, can make a person feel faint, dizzy, short of breath, or fatigued. If you experience these symptoms alongside a slow pulse, it is important to see a doctor immediately, warns Paul Wang, M.D., director of the Stanford Cardiac Arrhythmia Service.
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Some individuals may require a pacemaker, a device placed in the body to keep the heartbeat from getting too slow. “If your heart rate is slow and you feel dizzy and that you are about to pass out, it is important to see a doctor right away,” Dr. Wang explains.
Emergency thresholds and symptoms
Doctors set specific thresholds for emergencies. “A heart rate less than 35 beats per minute or greater than 150 beats per minute (at rest) should be considered an emergency,” says Dr. Victor, a cardiologist at Cardiology Consultants of Philadelphia.
High heart rates accompanied by chest tightness, palpitations, fainting, shortness of breath, or fatigue may suggest an arrhythmia. These symptoms combined with a fast or slow pulse require immediate medical attention.
Managing the rhythm
For immediate stabilization, deep breathing can be effective. “Deep exhalations can decrease your heart rate,” Dr. Wang advises. A technique of breathing in through the nose for a count of four, holding it, and exhaling deeply for a count of six can help lower the rate naturally.
Long-term management often involves aerobic exercise. “Consistent exercise stimulates the parasympathetic nervous system, which leads to a lower resting heart rate,” Dr. Wang says. Yoga, meditation, and breathing exercises can also help regulate the heart over time.
Know your baseline
Because heart rate varies significantly from person to person, it is key to know your personal “normal.” If you notice a significant change in your resting rate without an obvious cause—such as a change in activity level or medication—you should consult a healthcare professional.
More importantly, if a change in heart rate is accompanied by symptoms like lightheadedness, passing out, heart flutters, shortness of breath, or chest pain, seek medical help right away.
